Sequence of events which occur in a reflex action are

Options

A. Receptor - motor neuron - CNS - sensory neuron - effector muscle
B. Effector muscle - CNS - sensory nerve - sensory organ
C. CNS - sensory neuron - motor neuron - effector muscle
D. Receptor organ - sensory neuron - CNS - motor neuron - effector muscle

Explanation

To understand the sequence of events that occur in a reflex action, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Receptor Organ Activation**: The process begins when a stimulus is detected by a receptor organ (e.g., skin, eyes, ears). The receptor is sensitive to specific stimuli, such as heat, light, or pressure.

2. **Sensory Neuron Transmission**: Once the receptor is activated, it generates an electrical signal that travels along a sensory neuron. This neuron carries the information from the receptor to the central nervous system (CNS).

3. **Central Nervous System Processing**: The sensory neuron connects to the spinal cord (part of the CNS). Here, the information is processed. In a reflex action, this processing occurs quickly and does not involve the brain, allowing for a rapid response.

4. **Motor Neuron Activation**: After processing the information, the CNS sends a signal through a motor neuron. This neuron carries the command from the CNS to the effector.

5. **Effector Response**: The motor neuron connects to an effector (muscle or gland). The effector responds to the signal by contracting (in the case of muscles) or secreting (in the case of glands), resulting in a reflex action.

### Final Sequence:
- Receptor Organ → Sensory Neurons → CNS (Spinal Cord) → Motor Neurons → Effector Muscle